When producing rice and processed rice foodstuffs through cooking or heating, the immersion treatment is conducted. Because in immersion treatment the rice itself generally absorbs water, it is difficult to use chemical treatment. To make possible the safekeeping of rice in ambient temperature, the rice must be heat-processed long enough.
Heating rice at temperatures over 130° C. removes heat-resistant spore-forming bacteria but reduces the quality of rice. Therefore, an effective, nonchemical sterilization method is required that does not cause the deterioration of the quality of the processed rice.
JP Pat. No. 2626778 discloses that acid aqueous anode solution made from a weak saline solution electrolyzed through a diaphragm has germicidal power. However, the technique has problems in that a sufficient sterilization effect may not be obtained, and the odor and the low potential of hydrogen level (pH 1.5˜3.1) of the available chlorine, which serves as the principal sterilizing agent, reduces the quality of the processed rice.